In industry objects are conveyed from a production location on a conveyor such as a conveyor belt to a following location, where the objects are, for example, removed from the conveyor belt and then placed in a pack or a processing machine. In the food industry, for example, for the sake of hygiene, ergonomics and flexibility, these operations are increasingly being automated and performed by robots.
In the case of specific applications, such as, for example, the packaging of biscuits, sweets or sausages, the robots are used to remove individual products from a moving conveyor belt and, for example, to place them in a pack alongside the belt. This process is known as single picking.
Single-picking robots must have a working range which covers part of the length and the full width of the conveyor belt and some form of pack, such as, for example, a packaging box, when there is a robot standing on one side of the conveyor belt, or half the width when there is a robot standing on both sides of the conveyor belt, in order to ensure that at every desired position within that range individual products can be gripped on the belt and placed in some form of pack. For the speed of the operation in this application it is particularly important for the robot to have a gripper which can move at high speed across the width of the conveyor belt. It is also important for the robot to be sufficiently strong and to be able to withstand a certain load, produced by, for example, the weight of the product and the gripper.
It is known to use scara robots or delta robots for the single-picking application. An example of a scara robot is shown in FIG. 1. An example of a delta robot is shown in FIG. 2 and is known, for example from EP 0 250 470. One feature of these known types of robot is that they have robot arms which are hingedly mounted relative to the fixed environment and relative to each other, so that the movement of one robot arm results in a circular path of the gripper. In the case of these robots a linear movement of the gripper can be obtained only by simultaneous movement of several arms, which in practice means that two or more weights must be moved during the movement. A fast linear movement over a relatively great distance, namely the width of the conveyor belt, requires a fast movement of several arms. This is possible in practice only if the robot arms have a low mass inertia, which particularly as far as scara robots are concerned is not the case. In the case of delta robots the construction is often more fragile, so that the mass inertia of the aims is less of a problem than it is in the case of scara robots. However, the fragile construction considerably restricts the load to which the delta robot can be subjected, which means that the latter can be used only for gripping light objects with a light gripper. Since the present robots are therefore either strong and slow (scara robot) or fragile and fast (delta robot), their usability and practical application is limited.
A further disadvantage of the construction of the scara robots and the delta robots is that when one of the arms moves the remaining arms are subjected to a load by the reaction forces which have been produced. These loads can rise to a high level at high speeds, with the result that the arms have to be of a heavier design, which increases the mass inertia, and this in turn adversely affects the speed. Furthermore, some arms purely bear the weight of the other arms.
Another disadvantage of the known robots is that they have a circular working range. This means that there is always an effective speed component in the desired direction and a useless speed component perpendicular to it. In order to be able to reach all points within the working range at an adequate speed, the arms therefore have to be much longer than the width of the conveyor belt. Nevertheless, the speed achievable in the desired crosswise direction of the conveyor belt will not be able to reach the same level in the region farthest away from the robot that it can reach close to the robot.
Such a robot is known from DE 196 08 844. In the case of the known robot a drive device is provided on one end of the base. The drive device includes several motors which engage on toothed belts in order to drive the arm and the slide. The known robot has a gripper which is fitted on one side of the slide and therefore extends alongside the arm. In the case of this known construction torsional forces occur on the arm when a product is being lifted with the gripper, which leads to a heavier construction of the base, the arm and other parts of the robot, in order to enable them to offer resistance to these torsional forces. The heavier construction has an adverse effect on the speed of the robot.
An object of the invention is to provide an improved robot which is capable of working at higher speed.